The present invention relates to an ink ribbon for use in electrothermic non-impact recording, and more particularly to an ink ribbon comprising an electroconductive base layer and an electroconductive and thermal-transferable ink layer formed on the base layer, wherein the base layer comprises a binder resin and an electroconductive material dispersed in the binder resin, and the ink layer comprises a thermoplastic material and an electroconductive material such as carbon black, in which base layer and ink layer Joule's heat is generated when an image-delineating electric current is caused to flow therethrough, so that the ink layer is softened in an image pattern and can be transferred to a receiving surface, for example, to a sheet of plain paper.
Conventionally, a variety of ink ribbons have been proposed for use in electrothermic non-impact recording in which an ink ribbon containing or coated with a pigmented and thermal-transferable material is superimposed on a sheet of plain paper, and the thermal-transferable material is locally softened in image form in response to image-delineating electric current applied thereto by a recording electrode comprising multiple styli and a return electrode which are placed in contact with the ink ribbon, and the softened thermal-transferable material is then transferred to the plain paper as dots or lines.
For example, in Japanese Laid-Open Patent Application No. 49-38629, there is disclosed an ink ribbon comprising an electrically anisotropic base layer and an electroconductive ink layer. In the electrically anisotropic base layer, the electroconductivity varies with the direction through the base layer--i.e., in this case, the electroconductivity is greater in the transverse direction (normal to the surface) than in the superficial direction (parallel with the surface). This electrically anisotropic base layer is prepared by orienting a ferromagnetic metal powder dispersed in a molten binder resin in the direction normal to the surface of the base layer in a magnetic field. In this method, however, it is extremely difficult to attain uniform orientation of the metal powder over a large area.
In Japanese Laid-Open Patent Application No. 53-7246, there is disclosed another ink ribbon comprising an electrically anisotropic base layer and an electroconductive ink layer. This electrically anisotropic base layer comprises a binder resin and a metal powder dispersed in the binder resin. The most significant shortcoming of this ink ribbon, too, is that the metal powder cannot be dispersed uniformly over a large area, and, if there is a portion where the metal powder is coagulated, the flow of recording electric current becomes uneven in that portion and accurate recording cannot be done.
In Japanese Laid-Open Patent Application No. 56-8276, there is disclosed a further ink ribbon comprising an electrically anisotropic base layer and an electroconductive ink layer. The electrically anisotropic base layer comprises a silicone rubber and minute pin-formed electric conductors made of a metal or carbon embedded in the direction normal to the surface of the layer. The maximum image resolution that can be obtained by this ink ribbon is 4 lines/mm and it is not suitable for practical use.